The invention relates to a semiconductor integrated circuit device (IC) whose operating frequency can be checked easily using a simple testing apparatus.
A tester is used in different tests to measure and assess performance of an IC. The tests include, for example, DC test, switching test, and function tests. Assessment of performance includes measurement of operating frequency of IC.
Recent ICs are designed to operate at a high clock speed (or clock frequency), often in the range of 100-200 MHz. Performance of such high-speed IC can be assessed through various kinds of tests including a DC test, a switching test, and a function tests for example by analyzing an actual critical path of the IC (which is the longest path requiring the longest propagation time between the input and output ends of the IC) and establishing a function pattern for the critical path. This can be done by means of a tester which can respond to the high speed clock signal of the IC.
However, it is much too heavy a burden to provide a large number of such high speed testers in testing mass-produced ICs and innovate them to meet new testing requirements every time ICs are redesigned for an improvement in a short period. An analysis of actual critical path of an IC requires many hours, and so does establishing the function pattern of the IC. Furthermore, the analysis for the critical path and the formation of the function pattern must be redone every time the circuit is modified.
It is possible to perform many tests on an IC with a tester having a slower operating frequency than the IC. However, slower testers cannot measure the operating frequencies of the internal elements of an IC, that is, they fail to measure the propagation speed of a signal within an IC.
Therefore, it is an object of the invention to provide an IC equipped with speed measurement means capable of measuring the operating frequencies of the internal elements thereof using a tester having a slower operating frequency than the IC itself.
In accordance with one aspect of the invention, there is provided an IC having a multiplicity of elements, comprising:
a predetermined number of measuring elements connected in series to form an array; and
detection means for simultaneously detecting the electric potentials at a multiplicity of predetermined nodes of the measuring elements and outputting the detected potentials in numerical data.
The detection means comprises:
a multiplicity of latch circuits which operate in response to the latch signal; and
a decoder for receiving the outputs of the latch circuits and converting the outputs received into numerical data, which data is provided at the output terminal of the decoder.
The array of the measuring elements is supplied at the input terminal thereof with a propagation signal. The latch circuits are provided with a delayed latch signal a predetermined time later after the application of said propagation signal to the array.
As a result, the propagation of the signal, i.e. varying potential along the array is latched in the latch circuits simultaneously after a predetermined time subsequent to the application of the signal to the input terminal of the array. The latched propagation signal is output in the form of numerical data for the IC, which results in the propagation speed of the signal through the internal elements, hence the operating frequency of the internal elements. Hence, measurement of the operating frequency of an IC can be made by a tester operating slower than the IC.
In the invention, the IC is provided with a pulse signal generator which generates a propagation signal in response to an externally applied instruction signal and in synchronism with a given clock signal, and generates the latch signal delaying behind the propagation signal by a predetermined number of clocks. The pulse generator is configured to provide the decoder with a decode signal delaying behind the latch signal by an arbitrarily time.
Thus, by simply providing an instruction signal from an external device (e.g. tester) arbitrarily, a propagation signal is generated, which propagates along the array for an arbitrary number of clocks (e.g. 1 clock) in synchronism with the clock until it is latched in the latch circuits, thereby providing numerical information on the propagation of the signal.
The internal clock signal of the IC under measurement may be used as the clock signal for the measurement. In this case, no external clock for the measurement is necessary. Then the propagation speed of a signal in the IC operating at the nominal operating frequency is obtained directly from the measurement.
Alternatively, the clock signal may be provided by an external device having a desired operating frequency. In this case, frequency of the measurement is not limited to the frequency of the internal clock, that is, the measurement frequency can be arbitrary. In addition, a higher resolution of the measurement can be obtained by performing the measurement at different frequencies.
Buffers may be used as the representatives of standard elements of an IC.